A sample survey with the objective of determining the prevalence of
bovine tuberculosis by means of an intradermal tuberculin test was
conducted in Madagascar and it was found that the prevalence rate varied
from 0-30% by veterinary district. In order to estimate the true
prevalence, the validity of the test was investigated by assessing its
sensitivity and specificity in two groups of animals from two different
regions, which were destined for slaughter. In the first group where the
probability of non-infected animals should have been the highest,
sensitivity was estimated at 0.52 ( n=21) and specificity at 0.99 (
n=79). In the second group selected on the basis of apparent ill health
of the animals in a high-prevalence bovine tuberculosis area,
sensitivity was estimated at 0.8 ( n=10) and specificity at 1 ( n=12).
The results obtained from both groups of cattle were not combined for
statistical purposes because the sensitivity of the skin test seemed to
fluctuate in relation to the chronicity of the disease. These
fluctuations are discussed. However, since the first group of zebu
cattle was more representative of the cattle population across the
country as a whole, its results were retained as operational parameters
for further screening.
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